Effect of stimulation parameters on entrainment

The postpacing interval (PPI) may be longer ( . 30 ms) or even shorter ( , 0 ms) than the tachycardia cycle length (TCL) when entrainment pacing is performed within the isthmus of the circuit. 1,2 In this study

The postpacing interval (PPI) may be longer (.30 ms) or even shorter (,0 ms) than the tachycardia cycle length (TCL) when entrainment pacing is performed within the isthmus of the circuit. 1,2 In this study, we aimed to evaluate whether stimulation parameters can affect the PPI in typical (cavotricuspid isthmus-dependent) atrial flutter (AFL).
Twenty-one patients with typical AFL were included in the study. Each patient provided written informed consent to the study protocol, which was approved by the Institutional Ethics Committee (Research No. 2020FYYX032). The research reported in this paper adhered to Helsinki Declaration.
After confirmation of a typical AFL, entrainment pacing with different parameters was performed. Pacing trains were performed with different numbers of pacing stimuli (16, 24, and 32 basic S1S1 stimulations), different stimulation intensities (5, 8, and 10 mA), and different pacing rates (10 ms less than TCL, 20 ms less than TCL, 30 ms less than TCL).
Continuous variables (PPI-TCL) were compared using the paired t test or Wilcoxon signed rank test. P ,.05 was considered significant. All analyses were performed using SPSS Version 17.0 (SPSS Inc., Chicago, IL).
There was no significant difference in PPI-CL between 16 and 24 basic S1S1 stimulations (12.0 6 11.1 ms vs 12.2 6 11.0 ms, respectively; P 5 .55) and between 24 and 32 basic S1S1 stimulations (12.2 6 11.0 ms vs 11.4 6 10.4 ms, respectively; P 5 .05). This finding indicates that the number of pacing stimuli does not affect PPI. There was a significant difference in PPI-CL between stimulation intensities of 5 and 8 mA (11.4 6 10.5 ms vs 7.1 6 8.7 ms; P 5 .01) and between stimulation intensities of 8 and 10 mA (7.1 6 8.7 ms vs 3.20 6 7.6 ms; P 5 .01). An example is shown in Figures 1A to 1C. Figures 1D and 1E show the possible mechanisms. When stimulation intensity increases, more of the far-field tissue may be captured because of the virtual electrode and the downstream wavefront forming farther from the pacing site and then returning to the pacing site earlier. As a result, PPI is shortened. Despite the existence of variability in PPI, 3 we can clearly see this tendency. Although the difference observed when the entrainment parameters are changed can consist of only a few milliseconds, it could lead to misclassification of an entrained site when the PPI-TCL interval is close to the threshold of 30 ms. The possible mechanism and an example is shown in Figures 1F to 1I.
There was a significant difference in PPI-CL between pacing with 10 ms less than TCL and 20 ms less than TCL (9.3 6 5.9 ms vs 10.6 66.2 ms; P ,.001), and between pacing with 20 ms less than TCL and 30 ms less than TCL (10.6 6 6.2 ms vs 9.2 67.3 ms, respectively; P 5 .04). Faster pacing may lead to decremental conduction or concealed conduction, which may affect PPI. 4 In conclusion, PPI is related to stimulation intensity and rate. Increasing stimulation intensity may shorten PPI, and the fast pacing rate also may affect PPI.